Tributylphosphate (TBP) is a trisubstituted ester of phosphoric acid that plays a central role in numerous industrial processes. TBP is employed in flame retardant formulations, as a lubricant, and as a solvent in the synthesis of nitrocellulose used in the production of plastic films and as a binder in ink films and wood coatings. TBP is also employed in the agricultural chemistry field as a carrier solvent and de-foaming agent in a variety of pesticide and herbicide formulations. Its most notable application is as a means of extracting valuable actinide metals (such as uranium and plutonium for nuclear power applications) from ores or waste through the Plutonium Uranium Redox Extraction (PUREX) process which uses a combination of TBP and a hydrocarbon-rich matrix as a solvent for extraction and purification of actinide metals. Because no viable alternatives to TBP currently exist for this application and because the International Atomic Energy Agency currently expects worldwide nuclear power usage to increase by 17% to 94% by the year 2030 there will be an increasing demand for this hazardous material for the foreseeable future. Thus, environmentally-friendly, or “green”, disposal and neutralization methods targeting this chemical are necessary.
Tributylphosphate (TBP) is highly toxic and has an innate chemical stability that renders its destruction and disposal difficult thus resulting in its unwelcome and harmful persistence in the environment. Currently, methods to dispose of TBP are expensive, inefficient and the methods themselves are harmful to the environment. Incineration is the most employed technique for the breakdown of TBP into its elemental components, but must occur at high temperatures, up to 300° C. and, thus, is not cost effective. Alternative methods have been sought, but all remain expensive and thus are unrealistic for use. Acid and basic processes to dispose of TBP also require high temperatures and hazardous conditions (high acidity or alkalinity). Radioactive destruction methods of TBP are inherently hazardous and expensive. And finally, biological approaches to break down TBP involve a water-like environment which is ineffective for the oily mixture of TBP generated in the PUREX process. Moreover, degradation and disposal of phosphotriesters other than TBP suffer from similar challenges.
Accordingly, it would be desirable to efficiently convert TBP and/or other phosphotriesters to their more water-soluble salts (using, e.g. potassium, sodium, etc. as the counter-cation). In the case of TBP, it would be desirable to convert TBP to water-soluble salts, such as potassium dibutylphosphate (DBP) and potassium monobutylphosphate (MBP), using a method that is cost effective and not harmful to the environment.